1. Field of the Invention
The present invention relates to blade drive devices and optical apparatuses.
2. Description of the Related Art
In a device disclosed in Japanese Unexamined Patent Publication No. 8-289529, a shaft portion of a magnetic rotor is magnetized at a given polarity. The magnetic force is exerted between the shaft and a stator yoke, thereby applying a thrust-direction force to the rotor. This prevents a play in the thrust direction. Additionally, Patent Document 1 proposes that this device is employed in an aperture device of an optical apparatus
In the device disclosed in Japanese Unexamined Patent Publication No. 8-289529, the thrust-direction force has to be generated by the magnetic force. To this end, a sufficient strength of the magnetic force and a sufficient size of the device are required. Therefore, there is a problem of a large restriction in design, thereby making it difficult to slightly adjust the force. Further, the shaft portion has to be magnetized, so that a process for magnetizing the rotor may be complicated and the cost may be increased. Furthermore, the shape of the stator may be complicated.
To overcome the above problems, it is conceivable that the rotor is urged by an elastic member such as a spring so as to apply the thrust-direction force to the rotor. However, if the spring or the like is employed, the device itself may be increased in size in the thrust direction.
Besides, the conventional stepping motors do not stably stop every other pulse in the non-energized state. Stoppable positions of the aperture blades result in every other pulse. This raises a problem that the blades cannot be controlled at high speed with high accuracy.
In a case where the all pluses are respectively associated with the aperture diameters for the purpose of overcoming the above problem, there has been an aperture device. This aperture device maintains to apply a voltage, which is lower than that used in the driving, at positions where the blades cannot stop in the non-energized state. However, power consumption may be problematic.